3-Methyl-cyclopentadec-5-en-1-one is a macrocyclic ketone and an unsaturated homolog of muscone, a compound which is well appreciated in perfumery. Owing to the presence of a ring double bond, there are several possible position and configuration isomers for this molecule. The structure of some of them is known. Thus, the structure of the above-mentioned enone, as well as that of several of its isomers, has been described in the literature, mostly in connection with organic syntheses, namely that of muscone. However, there has been no mention of any possible useful odor properties for these compounds.
An exception is, however, patent U.S. Pat. No. 3,778,483 which describes a process for the preparation of muscone from unsaturated ketones of formula ##STR1## having a double bond of cis- or trans-configuration in one of the positions indicated by the dotted lines and wherein R represents hydrogen or a methyl radical, one of the n indexes has the value 1 and the other the value 2. The ketones of formula (I) are said to possess a stronger odor than that of their corresponding saturated homolog ketones. According to the inventors of the cited patent, the saturated ketones have a characteristic musky odor, while ketones (I) wherein R is hydrogen possess an odor reminiscent of that of civettone and those wherein R is a methyl have rather a woody odor.
In spite of the fact that several ketones (I), or mixtures of ketones (I), are cited in said patent, namely 3-methyl-cis-cyclopentadec-4-en-1-one (example 4) and 3-methyl-trans-cyclopentadec-4-en-1-one (example 17), as well as a mixture containing essentially the trans isomers of 3-methyl-cyclopentadec-4 and 5-en-1-one (examples 1 et 2), we were unable to find any description of the individual properties of any of these ketones or mixtures, or of the possible olfactive differences between them.
On the other hand, a more recent patent, i.e. GB 2 058 786, reports the preparation of unsaturated macrocyclic ketones of formula ##STR2## wherein the dotted lines designate the location of a single or double bond and wherein x=1 and y=2, or x=2 and y=1. Although the usefulness of the odor properties of ketones (II) is cited (see page 4, line 18), this citation is based on the above-mentioned prior art and no further description of the properties of 3-methyl-cydopentadec-4-en-1-one, described in example 5 and designated under the name of "muscenone", can be found in this document.
Finally, a textbook in perfumery, i.e. the book by S. Arctander, Perfume and Flavor Chemicals, Montclair, N.J., USA (1969), describes 3-methyl-cyclopentadecenone under section 1985, also designating it as "muscenone", to which is assigned the structure ##STR3## and the odor of which is said to be a "delicate, but extremely tenacious musky odor, upon dilution developing more woody notes, not quite as soft and velvety as those of the muscone, perhaps equal in power, but inferior in beauty" (sic). Curiously, the author also states that "it is inconceivable that this ketone will become a common musk at all" (sic).
Combined with a total lack of analytical characterization of the described compounds, which does not allow a precise teaching of the nature of the compounds and mixtures obtained according to the prior art, these poorly detailed and even somewhat contradictory olfactive descriptions, which moreover are not even supported by examples of perfumery applications, simply suggest that all unsaturated ketones of formula (I) or (II), homologs of muscone and Exaltone.RTM. (cyclopentadecanone; origin: Firmenich SA) possess similar odors, independently of the position or configuration of the double bond.
Yet we have now unexpectedly discovered that this is not at all the case and that, while all the ketones of formula (II) are indeed fragrant substances, their olfactive properties are quite distinct from one to the other, one of these ketones possessing particularly useful and unexpected properties.